diff -r 5d0d510d2db1 -r 40943970b7ae mercurial/branchmap.py
--- a/mercurial/branchmap.py	Mon Mar 04 04:13:33 2024 +0100
+++ b/mercurial/branchmap.py	Mon Mar 04 04:16:15 2024 +0100
@@ -732,7 +732,7 @@
 
         if self._names:
             try:
-                if repo.ui.configbool(b'format', b'mmap-revbranchcache'):
+                if repo.ui.configbool(b'storage', b'revbranchcache.mmap'):
                     with repo.cachevfs(_rbcrevs) as fp:
                         data = util.buffer(util.mmapread(fp))
                 else: